I’m taking a bit of time to brush up my knowledge of F# and see if I can write better F# code and one of the things I notice is that whilst I use pipe-forward operator (|>) often when working with collections I don’t nearly use the pipe-backward operator (<|) as frequently as I should. It makes sense as the pipe-forward operator works similar to the way LINQ and IEnumerable works, just to remind myself and others like me how these work:
Pipe-forward operator (|>)
Pipe-forward operator lets you pass an intermediate result onto the next function, it’s defined as:
let (|>) x f = f x
You can add further processing steps to this intermediate result:
Forward composition operator (>>)
The forward composition operator lets you ‘compose’ functions together in a way similar to the way the pipe-forward operator lets you chain function delegates together, it is defined as:
let (>>) f g x = g (f x)
Now imagine if you have two functions:
You can use them to build a high-order function that returns triples the square of a float, n, using the >> operator:
This is syntactically cleaner and easier to read than:
and it’s especially useful when chaining together a large number of functions.
Pipe-backward operator (<|)
The pipe-backward operator takes a function on the left and applies it to a value on the right:
let (<|) f x = f x
As unnecessary as it seems, the pipe-backward operator has an important purpose in allowing you to change operator precedence without those dreaded parentheses everywhere and improve readability of your code,.
can be written as
Backward composition operator (<<)
The inverse of the forward composition operator, the << operator takes two functions and applies the right function first and then the left, it’s defined as:
let (<<) f g x = f (g x)
Mostly I find it more suitable than the forward composition operator in cases where you want to negate the result of some function, for example, to find the odd numbers in a list:
I’m an AWS Serverless Hero and the author of Production-Ready Serverless. I have run production workload at scale in AWS for nearly 10 years and I have been an architect or principal engineer with a variety of industries ranging from banking, e-commerce, sports streaming to mobile gaming. I currently work as an independent consultant focused on AWS and serverless.
Here is a complete list of all my posts on serverless and AWS Lambda. In the meantime, here are a few of my most popular blog posts.
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